Brazing materials

ABSTRACT

An aluminum-silicon brazing composition containing about 0.02 to 0.20% bismuth by weight, with silicon in the range from about 7 to 14% and magnesium in the range from about 0.2 to 2%; preferably employed as a cladding layer on a magnesium-containing aluminum base core alloy.

limited States Patent 191 Singleton, Jr.

[ 1 BRAZING MATERIALS [75] Inventor: Ogle Singleton, .lr., Richmond,

[73] Assignee: Reynolds Metals Company,

Richmond, Va.

[22] Filed: May 25, 1973 [21] Appl. No.: 363,910

[52] 10.8. C1 75/147, 75/141, 75/142, 75/ 146 [51] Int. Cl C22c 21/00 [58] Field of Search 75/141, 146, 147, 148, 75/142 I [56] References Cited UNITED STATES PATENTS 1,453,928 5/1923 Edwards 75/148 11] 3,853,547 [4 Dee. w, 1974 1,932,848 10/1933 Dean 1,986,825 1/1935 Kempf 75/147 2,766,116 10/1956 Schlucter 75/147 3,226,267 12/1965 Foerster 75/138 3,466,170 9/1969 Dunkel 75/147 Primary Examinerl-lyland Bizot Attorney, Agent, or Firm-Glenn, Palmer, Lyne & Gibbs [5 7] ABSTRACT 7 Claims, No Drawings This application concerns an improved aluminumsilicon brazing composition for joining aluminum alloy components, and containing about 0.02 to 0.20% bismuth by weight. The silicon content ranges from about 7 to 14%; and the composition also contains about 0.2 to 2% magnesium. In a particularly effective embodiment, this brazing composition is employed as the outer cladding layer on a higher strength aluminum alloy core component, preferably a core alloy of the type containing one or both of magnesium and maganese in amounts up to about 3% magnesium and up to about 1.5% manganese. 1

Aluminum-silicon alloys have been used previously for brazing, and those further containing magnesium have been used for vacuum brazing. An unsolved problem has been to find a brazing composition capable of tolerating pressure variations commonly encountered in commercial vacuum brazing operations, anad effective at relative mild vacuums on the order of or even 10 torr.

In accordance with the present invention it has been found that a brazing composition consisting essentially of aluminum, silicon, magnesium and bismuth, in the amounts previously noted, has especially desirable properties for purposes of vacuum brazing. That this result obtains is surprising and unexpected, because bismuth, although reported in the literature as being a helpful addition to Al-Si brazing compositions used in an inert-gas environment at atmospheric pressure, has exhibited a negative effect on the vacuum brazing behavior of Al-Si compositions which do not contain magnesium. Hence, there appears to be some sort of potentiating effect due to the presence of both bismuth and magnesium in Al-Si compositions of the type described herein.

include 3105, 3003, 3004, 5005, 5052 and 5457. Preferred core alloys are those containing 0.1 to 3% magnesium and up to about 1.5% manganese, typically about 0.3 to 0.8% manganese, balance aluminum and incidental impurities or minor alloying elements in amounts up to about 0.8% iron (typically 0.2 to 0.7%), 0.8% silicon (typically about 0.25 to 0.5%), 0.4% zinc, 0.35% chromium, 0.4% copper, 0.1% titanium, with others not exceeding 0.05% each and 0.15% total. With respect to these core alloys amagnesium content of about 0.2 to 0.8% is usually sufficient, sometimes as little as 0.2to 0.4% in connection with an alloy having a nominal composition of approximately 0.3% Mg and 0.4% each of silicon, iron and manganese.

EXAMPLES The following examples illustrate the practice of the invention and its presently preferred embodiments:

EXAMPLE 1 The nominal chemistry for the four plant produced brazing sheets and surface oxide thicknesses are given in Table l. The chemistry of laboratory produced composites and surface oxide thicknesses are given in Table 2.

" 3003 nominal 0.12% Cu, 1.2% Mn R396 nominal 0.15% Cu, 0.2; Mn, 0.22% s X-7 brazing sheet (X4004 cladding) (a) Core alloy RX606 nominal 0.4% Si. 0.4% Fe. 0.4% Mn. 0.3% Mg The brazing material may be used as a separate component, such as a shim or in the form pfwire or rod, but is preferably applied as the cladding on aluminum alloy components to be joined by vacuum brazing. The cladding may be on one or both sides of the core component, and typically constitutes from about 5 to about 15% of the composite thickness. Suitable core alloys TEST SPECIMENS AND EVALUATION l. The Gap-Joint Specimen An assembled, ready-for-brazing, gap-joint test specimen was prepared from 3003 fin stock one-half inch high so that seven nodes of fin stock support the brazing sheet specimens. A suitable length of 24 gage (0.0201 inch dia.) EC wire was placed centrally between the strips of brazing sheet to create a gap.

The brazing sheet to be tested was used as four strips 0.020 X A X 3 inches with a pair of holes 2% inches apart, one of the holes being spaced three-eighths inch from an end. The four strips were then paired up, holes matching but ends not in registry. This arrangement permitted each pair of specimens to be held together by screws and yet provided endjoints.

The EC wire formed a gap in the one-half inch wide lap joint. This gap extended about five-eighths inch to either side of the wire; thus four, lap-joint gaps were provided each of which was similar to, but larger than,

vthe gaps known to occur in production assemblies.

The main evaluation is the number of these 4 gaps which are sealed by brazing flow as a measure of the amount of flow which occurred in the gaps. The goal is to seal all four gaps during brazing.

II. The Three-Tiered Joint Four pieces of brazing sheet -l inches square were separated by three rings of seven-eighths inch o.d.,

PROCEDURE Brazing sheet was oiled if handled by hand. Prior to assembly, all components were solvent degreased in perchloroethylene. After solvent degreasing, gloves were used to avoid fingermarks (a possible joining variable) on the material.

The test specimen was mounted on a thin, stainless steel carrier. The carrier was attached to a one-eighth inch o.d. stainless steel sheathed, type K, thermocouple. The grounded junction occupied a position between the brazing sheet pairs of a gap joint. The sheathed thermocouple extended through an O-ring seal in the removeable furnace door.-

The non-contact thermocouple was used to estimate specimen temperature. This method of temperature assessment was used because it was thought it would insure repeatability of both temperature and brazing results.

A typical brazing cycle consisted of the following steps:

I. Vent furnace to air; furnace hot zone at temperature.

2. Remove blank-off furnace door.

3. Slide specimen carrier into warm (300 to 500F) zone of furnace, secure furnace door.

4. Pump furnace to desired vacuum and hold using throttling valve.

5. Using sheathed thermocouple as a push rod, insert sample into the hot zone.

6. Record thermocouple output, and system pressure during brazing cycle; continue to hold pressure with the throttling valve.

7. Arbitrarily, limit brazing cycle to l minutes.

8. Again, using the sheathed thermocouple, withdraw the specimen to the furnace warm zone.

9. When the thermocouple indicates less than 800F,

vent the furnace to air, remove the door with specimen carrier and brazed joint.

10. Replace blank-off door and pump down the fur-- nace.

The brazed specimen was then cooled, removed from the carrier, sampled for surface chemistry, and evaluated visually.

The sole measure of brazing environment was pressure. Pressure was measured either with a NRC 527 ion gage and a 710 controller or a Hastings DV6 gage and meter. The environmental pressure was changed by throttling a gate valve to the vacuum pump. The pressure sources were such actual and virtual leaks as existed at a given time plus off-gassing particularly from the specimen and jib.

Surfaces were sampled for determination of postbraze oxide film thickness and surface magnesium. The gap-joint was always sampled'on the top surface near an end. The three-tiered specimen was sampled on both inner and outer surfaces. Determinations were made using the electron microprobe. Oxide film thicknesses (Acet) were determined for the 0.020 inch (:.002 inch) clad sheets, and expressed in Angstroms on the basis of counts for equivalent thickness relative to reference oxide films of known thickness on 99.99% aluminum.

RESULTS AND DISCUSSION The following results are based on numerous vacuum brazing tests using the various brazing sheets. The objective of these tests was to rate each brazing sheet on the basis of its ability to seal gaps. Some alloys were also rated for joining in a closed member using the three-tiered joint test. For purposes of comparison, a torr (equal to 1 mm Hg) corresponds to a pressure of 10 microns.

l. The Three, Plant-Produced MD Alloys A) Gap-Joint Tests The three metallurgical development alloys were MD150, MDl76, and MDl77. On the basis of gap-joint test results obtained with these alloys MD I 76 and MDl77 behaved quite similarly. At 40 to 50 microns, none sealed even one gap; surfaces after brazing were dull; all postbraze oxide thicknesses were over 300 Acet. None sealed 4 gaps in the 20-30 micron range; however, post-braze oxide values were reduced, particularly for MDl77.

In the low micron pressure range, MDl77 seemed more consistent in gap-filling ability and superior to MDl76 in that respect. It is significant that MDl77 is cored with magnesium-containing R396 alloy while MDl76 is cored with 3003 which contains no magnesium. With three exceptions, the post-braze oxide film thicknesses were all under 150 Acet. when brazed at pressures under 12 microns. All three exceptions were with MDl77.

The MDlSO used came from formed, commercial evaporator plates except for three joints which came from an accepted lot" used in other tests. MD150 appeared to function well only at a decade or decade and a half lower pressures than did MDl77. That is, gap filling was erratic in the high 10" torr pressures and generally poor in the micron pressure range. This result is in good agreement with tests on full-size evaporators. Postbraze oxide thicknesses were similar to those obtained on the other alloys. With four exceptions, the thicknesses were under 150 Acet below 20 microns, ranged from to 400 Acet in the 20 microns and were above 400 Acet at pressures in the 40 microns.

Only MDlSO and MDl77 were tested in the 10' torr range. As was expected, all three alloys sealed all four gaps. The post-braze oxide-film thicknesses were to 91 Acet for MDl50, and below 50 Acet for MDl77.

What appeared to be slight erosion of the core was encountered in MDl77. Based on our laboratory experience with RX606. it was thought that erosion would over the present,

sion was due to the relatively high purity of R396.

commercial vacuum-brazing sheet X7 (MD150). That is. these materials produce brazing alloy flow that will seal gaps up to several microns pressure, a much poorer vacuum than B) Three-Tiered Joint Test 5 MD150 will tolerate and still seal a gap.

The three tiered joint test was concerned with fillet The i of 01% i to aIummUm'SIhCPn' behavior on both the inside and the outside of the magnesmm Yacuum brazmg'anoys produced an i structure. Sealing of the vent slot was noted as another 5 m pressure tolerange for gap'sealmg test observation. The results of testing MD150 and CW whlch was so marked a It was unexpectd MD177 in this configuration are given in Table 3 be- The use ofan alloy Such as R396 or RX606Wh1ch not be a problem with an RX606 core, and that the erolow contains magnesium, improved the brazeability of TABLE 3 Summary of Three-Tiered Joint Results Brazing lnner Outer MD Pressure Temp. Fillet Fillet Vent Alloy Torr Exp."" F Rating Slot 177 4.5-3 3 1110 l 1 Sealed 177 12-2 -5 ll 10 l 1 Sealed 177" 12-3 5 ll 10 l 1.2 Partially Filled 150" 12-3 5 1110 5 1,2 Open exponent of 10 1, full. smooth continuous; 2. full. rough continuous; 3. small continuous; 4. slight skip; S. skips the 3003 spacers were degreascd but not chemically cleaned.

The surface chemistry of these samples was obtained on both inside and outside surfaces. These results are given in Table 4 which follows:

the composite as compared to brazing sheet cored with 3003. The R396 core of MD177 showed signs of erosion in laboratory tests; RX606 core alloy has TABLE 4 Three-Tiered Joint Surface Chemistry exponent of 10 The 3003 spacers were degreiiscd hut not-chemically cleaned.

The exterior surface chemistry was essentially that of the gap joints. The interior showed much thicker oxide films as have been found on other enclosed region specimens. There did not seem to be a correlation between surface chemistry inside the joint and filleting inside the joint, e.g. the MD150 had the thinnest, intenot evidenced erosion and thus would seem the better choice for a core alloy technically as well as economically. I r What is claimed is: 1. An improved brazing composition effective for joining aluminum alloy components by vacuum brazing rior oxide film and the poorest fillets.

The foregoing results show the superior performance of MD177 in both the gap joint tests and in this test.

11. The Four, Laboratory Produced Alloys A)'Gap Joint Tests The four laboratory produced alloys had brazing compositions containing 0 Mg; 0.3 Mg; 0.3 Mg 0.1

Bi; and 0.7 Mg 1.6 Zn.

Two major points are apparent from the results obtained. First, the addition of 0.1% bismuth to the 0.3 Mg alloy remarkably improved the gap filling ability of brazing sheet having a 0.3 Mg 0.1 Bi cladding on a alloys.

CONCLUSIONS 1. MD177 and MD176 offer improved brazeability consisting essentially of aluminum, about 7 to 14% silicon, about 0.2 to 2% magnesium and about .02 to 0.20% bismuth, by weight, with minor elements and impurities in amounts up to about 1% iron, 0.2% copper, 0.25% manganese, 0.6% each in the case of zinc and titanium, others not exceeding 0.05% each and 0.15% total.

2. The brazing composition of claim 1 containing about 0.1% bismuth.

3. The brazing composition of claim 2 containing about 0.3 to 1.5% magnesium.

4. The brazing composition of claim 1 containing up to about 0.3% iron.

5. The brazing composition of claim 1 containing up to about 0.2% zinc.

6. The brazing composition of claim 1 containing up to about .05% titanium.

7. The brazing composition of claim 1 containing about 9 to 11% silicon, about 0.3 to 1.5% magnesium and about 0.1% bismuth. 

1. AN IMPROVED BRAZING COMPOSITION EFFECTIVE FOR JOINING ALUMINUM ALLOY COMPONENTS BY VACUUM BRAZING CONSISTING ESSENTIALLY OF ALUMINUM, ABOUT 7 TO 14% SILICON, ABOUT 0.2 TO 2% MAGNESIUM AND ABOUT .02 TO 0.20% BISMUTH, BY WEIGHT, WITH MINOR ELEMENTS AND IMPURITIES IN AMOUNTS UP TO ABOUT 1% IRON, 0.2% COPPER, 0.25% MANGANESE, 0.6% EACH IN THE CASE OF ZINC AND TITANIUM, OTHERS NOT EXCEEDING 0.05% EACH AND 0.15% TOTAL.
 2. The brazing composition of claim 1 containing about 0.1% bismuth.
 3. The brazing composition of claim 2 containing about 0.3 to 1.5% magnesium.
 4. The brazing composition of claim 1 containing up to about 0.3% iron.
 5. The brazing composition of claim 1 containing up to about 0.2% zinc.
 6. The brazing composition of claim 1 containing up to about .05% titanium.
 7. The brazing composition of claim 1 containing about 9 to 11% silicon, about 0.3 to 1.5% magnesium and about 0.1% bismuth. 